Glass tubulature for feeding mercury



Oct. 28, 1952 M. PIPKIN GLASS TUBULATURE FOR FEEDING MERCURY Filed Dec. 16. 1947 Patented Oct. 2.8,` 1952 GLASS TUBULATURE FOR FEEDING MERCURY Marvin Pipkin, cleveland Heights, ohio, assignor to General Electric Company, a corporation of New Yorkv Application December 16, 1947, Serial No. 791,993

2 Claims. Y (Cl. 13S-68) My invention relates to enclosures or containers which are to be filled with a measured small quantity of mercury, and more particularly to a glass tubulature or tubulated stem for such containers through which the measured quantity of mercury is introduced into the container.

In the manufacture of gaseous electric discharge devices or fluorescent lamps according to present methods, it is common practice to introduce the measured quantity of liquid mercury with which the lamps are filled, into the lamp envelope through the glass exhaust tube thereof while the lamp is still in the exhausting machine. Due to the heated condition, among other things, of the glass exhaust tube resulting from the heating of the lamp envelope during ,the` exhausting operation, the entire measured quantity of mercury does not pass freely through the kexhaust tube into the lamp envelope. Instead, a considerable portion of the mercury sticks to and remains on the inner wall of the glass exhaust tube due to condensation or mechanical adherence of the mercury, thereby resulting not only in a possible deciency of mercury withinothelamp but also causing an 'unnecessary waste of mercury.

To overcome this adherence of the mercury to the glass surface of the exhaust tube, it has been customary to provide such glass exhaust tubes with frosted interior walls. However, while this measure does effect some reduction in the amount of mercury retainedin the exhaust tube as compared to that retained within a clear glass or unfrosted exhaust tube, nevertheless a considerable quantity of mercury still adheres to the inner Wall of such inside frosted exhaust tubes. In addition, the frosting of such exhaust tubes is a relatively expensiveas well as hazardous operation.

It is one object of my invention, therefore, to provide a glass tubulature for a container or lamp envelope through which a measured quantity of liquid mercury may be introduced into the container, said tubulature having its inner wall surface of such characterfas to substantially prevent or at least greatly minimize adherence of the mercury thereto.

Another object of my invention is to provide a stem for an electric device having a glass exhaust tube extending therefrom, the inner wall surface of said exhaust tube being of such character as to substantially prevent adherence thereto of liquid mercury upon passage thereof through the tube.

A feature of the invention is the provision, on the inner wall surface of the glass tubulature or exhaust tube, of a thin, uniform `'and adherent coating cfa finely powdered material to minimize adherence of mercury to the said inner wall Surface, the powder material being of unctuous character and being-preferably applied to the tube Wall by being dusted thereon.

Further objects and advantages of my invention will appear from the following description of a species thereof and from the accompanying drawing in which:

Fig'. 1` is a longitudinal View, partly in section, of an envelope assembly for an electric discharge lamp having an exhaust tube accordingvto the invention for introducting mercury into the envelope; and Fig. 2 isa chart showing the frequency of distribution of mercury retained in glassexhaust tubes accordingto the invention as compared to exhaust tubes having insidefrosted and clear glass interiors, respectively.

Referring to the drawing, I have there shown my invention in connection with the manufacture of electric discharge lamps or similar devices such as fluorescent lamps in general use at present.

The lamp illustrated comprises an elongated tu-v bular envelope I of glass provided at each end thereof with a reentrant stem tube vi. having a seal portion 3. The interior of the envelope I may be provided with a coating II of a suitable fluorescent material such, for instance, as zincberyllium silicate. A thermionic electrode 4, such as a coiled coil tungsten vfilament coated with a suitable electron emissive materialsuch as bar-v ium oxide, is mounted Awithin theenvelope I at each end thereof, each electrode 4 being supported by a pair of current supply or leading-in wires 5, 6 connected to opposite ends of the electrode and sealed into the seal portion 3 of the stem 2. An exhaust tube'I is alsosealed at onev end into the seal portion 3 of one of theA stems 2, as shown in the drawing. The interior passageway 8 of. this exhaust tube is open through the seal portion 3 of the 4stern 2 tov thereby provide an unobstructed passageway communicating with the interior of the lamp envelope I. Through this passageway 8, a measured vquantity, 9 of mercury is introduced into the envelope I.

In accordance with the invention, the interior.

wall of the exhaust tube 'I is provided with'a thin,

uniform and tightly adherent coating I0 of a iinef powder material of unctuous character, preferably magnesium trisilicate of the approximate lled with a smoke of the powder material under a slight pressure, for instance, 3 lbs. pressure or thereabouts.

For the production of a satisfactory coating I9 of the powder material by such a dusting-on process, the powder material employed should be of very fine particle size and of a character such as t cohere well and form agglomerates. In particular, magnesium trisilicate powder having an average particle size of around 1 micron or less and which readily agglomerates has been found to produce a very satisfactory coating for the purpose of the invention.

Following the application of the powder material to the interior wall of the exhaust tube 1, the loosely attached powder particles are preferably removed from the tube wall in asuitable manner, preferably by rdirecting a jet of air through the tube at a suitable pressure, or connecting the latter to a vacuum, or both. 'I'he pressure of the air jet lemployed is preferably equal to twice, or slightly more than twice that of the atmosphere, e.v g., 18 lbs. gauge pressure, so as to approximate the actual pressure conditions which exist in the tube when the latter is first opened to the exhaust line on the lamp exhaust machine. Such removal of the loose or excess powder particles from the exhaust tube interior thus leaves a uniform film or layer I9 of fine, tightly adhering powder on the tube interior which film otherwise might be scrubbed 01T to an appreciable extent by the loose powder particles when the exhaust tube is first opened to the exhaust line on the lamp exhaust machine.

Exhaust tubes 'l provided with a coating I0 in accordance with the invention retain a considerably lower percentage of any given dose of liquid mercury, upon passage thereof through the tube, as compared to that retained by insidefrosted glass exhaust tubes or by clear (uncoated or unfrosted) glass exhaust tubes. Thus, comparative tests show that exhaust tubes 1 provided with a dusted-on air-cleaned coating I 9 of magnesium trisilicate retain on the average less than of the mercury dose whereas insidefrosted tubes retain on the average over 40% and clear glass tubes retain on the average over 80% of the mercury dose. Most important, however, is the marked improvement in the frequency distribution of the mercurir retained in the coated exhaust tubes according to the invention as compared to that occurring in clear glass and inside-frosted exhaust tubes, as shown by the charts in Fig. 2. Referring to Fig. 2, it will be seen that 100% of exhaust tubes provided with an air-jet cleaned magnesium `trisilicate coating I 0 in accordance with the invention (chart A) retained less Vthan 15 ings. or 29% (actually no more than 12.2 mgs. or about 24%) of an average 51.5 mg. mercury dose, whereas only 3% of inside-frosted (chart B) and 0% of clear glass exhaust tubes (chart C) retained less than 15 mgs. or 29% of the same 51.5 mg. average mercury dose.

In addition to their much lower retention of mercury, the coated exhaust tubes according to the invention can be produced with less hazardous manufacturing procedures and at considerably lower cost than the inside-frosted glass exhaust tubes customarily employed heretofore. While the coating l0 is preferably applied on the exhaust tube interior before the tube is sealed to the stem tube 2, it may, if desired, be applied after the exhaust tube has been sealed to the stem tube, i. e., after the lamp stem is completed.

In manufacturing a lamp cf the type described in connection with the drawing, an exhaust tube l provided with an interior coating I9 according to the invention is assembled with a stem 2, leading-in ,wires 5, 6 and electrode 4 to form a complete stem mount. This stem mount is then sealed to an end of the lamp envelope l the other end` of which is sealed by a similar stem mount which, however, may or may not be provided with a residue of exhaust tubing. After evacuation of the lamp envelope, but While it is still in the exhaust machine, the desired quantity of mercury is fed or dropped through the exhaust tube l, as `shownby the arrow in the drawing, into the lampl envelope l. The exhaust tube is then sealed or tipped-olf adjacent the stem seal portion 3 to thereby hermetically seal the lamp envelope. The envelope `is then provided at each end with suitable bases having contact terminals, to which terminals the electrode lead-in wires 5, B are connected.

While I have shown and described my invention in connection with the manufacture of an electric discharge lamp, it should be understood that itcan be applied equally as well to the manufacture of any other mercury-containing device where it is necessary to introduce a measured quantity of mercury into the device by means of a glass tube which is in a heated condition during the mercury-introducing operation.

What I claimas new and desire to secure by Letters Patent of the United States is: l

1. A stern for an electric device comprising a glass stem tube and a glass exhaust tube sealed to said stem tube and having a passage extending therethrough, said exhaust tube having its interior surface provided with a substantially uniform coating of an unctuous pulverulent material to which mercury is substantially nonadherent whereby to minimize retention of liquid mercury on the said surface upon passage thereof through the exhaust tube.

2. A stem as set forth in claim 1 wherein the coating on the interior surface of the exhaust tube consists of ne magnesium trisilicate powder.

MARVIN PIPKIN.

REFERENCES CITED The followingreferences are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 762,178 MacFadyen June 7, 1904 865,367 Edison Sept. 10, 1907 1,791,624 Jessup Feb. 10, 1931 1,830,598 Fagan Nov. 3, 1931 1,991,774 Spencer Feb. 19, 1935 2,063,835 Billson Dec. 8, 1936 2,129,296 Wurstlin Sept. 6, 1938 2,188,901 Hyatt et al. Feb. 6, 1940 2,192,869 Pearce Mar. 5, 1940 2,336,946 Marden et al. Dec. 14, 1943 2,421,975 Williams June l0, 1947 2,468,221 Miller Apr. 26, 1949 2,550,658 Van Dyke Apr. 24, 1951 FOREIGN PATENTS Number Country Date 655,422 France Apr. 18, 1929 OTHER REFERENCES 

